Electromagnetic circuit

ABSTRACT

An electromagnetic circuit with a yoke and a movable armature in a channel of a coil, with one end of the armature pivoted against one end portion of the yoke and with the other free end of the armature forming a working airgap with the yoke. The yoke has a substantially flat shape with a notch or an aperture for the coil to nest in so that the coil channel and the armature are situated substantially at one side of the flat yoke and the working airgap is outside of the coil.

United States Patent J arnbrink et al.

ELECTROMAGNETIC CIRCUIT Inventors: Karl Evert Jarnbrink, Grumsgatan 5,123 I 44 Farsta; Rolf Albin Zander, Storhagsvagen 28 A, 125 32 Alvsjo;Per Harry Elias Claesson, Osterhagens Gard, 142 00 Trangsund, all ofSweden Filed: Feb. 27, 1970 Appl.No.: 14,941

Foreign Application Priority Data Mar. 4, 1969 Sweden ..2931/69 US. Cl..335/270, 35/276 Int. Cl. .335 7/08 Field of Search ..335/270, 274,276, 279

[ Jan. 18, 1972 [56] References Cited UNITED STATES PATENTS 3,178,5324/1965 Smith ..335/276 X 3,253,195 5/1966 Fisher et al. .J ..335/2763,260,818 7/1966 Fisher et a]. ..335/274 X Primary Examiner-G. HarrisAttorney-Strauch, Nolan, Neale, Nies & Kurz [5 7] ABSTRACT Anelectromagnetic circuit with a yoke and a movable annature in a channelof a coil, with one end of the armature pivoted against one end portionof the yoke and with the other free end of the armature forming aworking airgap with the yoke. The yoke has a substantially flat shapewith a notch or an aperture for the coil to nest in so that the coilchannel and the armature are situated substantially at one side of theflat yoke and the working airgap is outside of the coil. I

7 Claims, 6 Drawing Figures mnucumwm 3.636.487

INVENTORS KARL EVERT JARNBRINK ROLF ALB/N ZANDER PER HARRY ELIAS CLAESSN MW,M, By YW ELECTROMAGNETIC CIRCUIT BACKGROUND OF THE INVENTION Theinvention relates to the type of electromagnetic circuits that areparticularly well suited for miniature relays with very small dimensionsand preferably intended for mounting on printed circuits boards. Theheight of the relay measured from the board must be small, preferablycorresponding to the height of a transistor which is less than mm., forexample 8 mm.

A primary object resides in providing a simple but effective novelelectromagnetic circuit adaptable for miniature relays providing smalldimensions and good operating characteristics.

A further object of the invention resides in providing a magneticcircuit having a flat planar yoke member with parallel end portions andat least one side portion adjoining the ends of the two end portions, acoil disposed adjacent the yoke side portion and between the yoke endportions with its axis parallel to the side portion and the centeropening or channel through the coil disposed to one side of the flatplanar configuration of the yoke, and a movable armature memberextending completely through the coil with one of its ends pivotedagainst one of the yoke end portions and the other armature endextending beyond the end of the coil to a disposition adjacent a planarside face of the other end portion of the yoke for movement toward andaway from the other yoke end portion, being so situated to provide aworking airgap located outside of the coil.

Still another object, in conjunction with the previous object resides inproviding the yoke with two spaced-apart side portions adjoining the twoend portions to provide a planar flat box frame yoke structure withinthe central opening of which, a part of the coil is disposed andadjacent oneof the fiat planar yoke faces the armature is disposed.

A still further object resides in an electromagnetic circuit made inaccord with either of the previous two objects and in combination withminiature relay contacts to provide a miniature relay with low-thicknessprofile suitable for printed circuit application.

Further novel features and other objects of this invention will becomeapparent from the following detailed description, discussion and theappended claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS A preferred structural embodiment of thisinvention is disclosed in the accompanying drawings, in which:

FIG. 1 is a top view of a part of the magnetic circuit according totheinvention,

FIG. 2 is a corresponding view of another part of the circuit,

FIG. 3 is a sectional view of the assembled circuit,

FIG. 4 is another sectional view taken at a right angle to the view ofFIG. 3,

FIG. 5 is an outer top view of the assembled circuit, and

FIG. 6 is an outer side view of the assembled circuit.

In the figures, reference numeral 1 designates the stationaryferromagnetic part or the yoke of the magnetic circuit. Referencenumeral 2 designates the moving part or the armature.

Reference numeral 3 designates the bobbin of the magnetizing coil. Thewinding of the coil is connected to terminals 10.

In the illustrated embodiment, the electromagnetic circuit 1,2,3 is usedin an electromagnetic relay, and hence it is provided with a number ofcontact spring groups, the springs 12 of which are connected toterminals 13.

As will be evident from FIG. 6, all terminal pins l0, 13 project fromone side of the relay. The terminals 10, 13 are intended to be connected(e.g., by soldering) to different parts of a printed circuit board.

In assembling the device, the yoke l is inserted between projections 4of the bobbin 3 and is turned towards the part 9 on the coil bobbin. Theyoke l is pressed against the part 9 by a clip 5 provided with two legs,and so designed that it presses the yoke 1 and the part 9 of the bobbinagainst each other with high pressure. There are two slots in the coilbobbin into which the legs of the clip 5 are inserted. The ends of saidlegs are going through the slots to the opposite side of the coil bobbin3 and are bent as indicated by reference numeral 5a in FIG. 5, in orderto keep the clip 5 in place. Preferably, the slots in the bobbin have awidth which allows the bent portions of said legs to be insertedtherein. In that case the clip 5 may be prebent before assembling. Uponassembling, the clip snaps into the locking position indicated in FIG. 4where it clamps the stationary ferromagnetic part 1 against the portion9 of the coil bobbin 3, and the bent portions 5a of the legs engage thebottom surface of the coil bobbin part which they penetrate.

One end of a leaf spring 6 is fixed to the annature 2'as shown in FIG.4, for example by spot welding. The other end of said spring is bentfrom the armature as shown and engages the inner, upper surface of alongitudinal opening in the bobbin 3, for keeping the armature in itsrest position shown in FIG. 4. In this position the narrow end of thearmature 2 is in pivoting engagement with the adjacent edges of the yokeI. The opposite broad end of the armature is kept at a distance from theopposite end of the yoke l for forming a working airgap 7 between saidbroad end of the armature and said end of the yoke.

As will be evident from the figures, the yoke is shaped as asubstantially plain, preferably rectangular frame, enclosing the coil.At one short side of said frame one of the ends of the said armature ispivoted and at the opposite short side of the frame, between said frameand the armature, the airgap 7 is formed. The two long sides of saidframe which constitute connecting members between its two short sides,are located along the sides of the coil, in the longitudinal directionof the latter. Also the armature is substantially plain and has a widthbigger than its thickness. The yoke and the armature are sub stantiallyparallel to each other and so arranged, that their adjacent surfacessubstantially coincide when the armature is operated. One of the longsides of the yoke which is located at one of the sides of the coil canbe dispensed with, in which case the whole magnetic flux has to passthrough the other side.

Furthermore, one projection 8 is provided at the end of the bobbin,which is adjacent to the airgap. When the armature is in its restposition shown in FIG. 4, it rests against said projection 8. Saidprojection 8 and the inner bottom surface of the longitudinal opening inthe coil bobbin 3, against which the armature 2 falls when the relay isdemagnetized, has a damping effect on the movement of the armature and,therefore, prevents bouncing of the armature upon demagnetization of therelay.

Preferably, there are two contact spring groups 12, viz one at each sideof the coil. Said contact spring groups are fastened to the long sidesof the yoke l in any suitable way, e.g., by screwing or glueing.

There is one actuating rib ll of insulating material fastened to eachside of the broad end of the armature 2 and arranged to cooperate withthe moving spring of said contact spring groups, so as to transmitmovement from the armature to said springs.

It should be mentioned that with a test relay manufactured according tothe foregoing description and which had a height of 7.5 mm. measuredfrom a printed circuit board onto which it was mounted, a length of 28mm. and a width of 20 mm., a traction force of approximately 200 gramswas obtained when the working airgap was 0.3 mm. and the magnetizingcoil was supplied with an electric power of 1.4 w. This surprisinglyhigh traction force is obtained because of the extremely big area,around 15 mm, in relation to the size of the relay, of those parts ofthe magnetic circuit (the armature and the yoke) which are passed by themagnetic flux generated by the current through the coil. Said area canbe still more increased by making the relay broader. Because thearmature 2 has a pole piece (the broad end of the armature) with aneffective area which is big in relation to the area of the armature andthe yoke which are passed by the magnetic flux, said area of the yokeand armature can be fully utilized, i.e., magnetic saturation can beallowed to occur when the power dissipation in the coil has such a valuethat the normal allowable temperature rise in the coil is obtained.

In the test relay having the dimensions stated in the foregoing, thetemperature rise in the coil was approximately 45 C. when thedissipation in the coil was 1.4 w. With this power dissipation in thecoil, saturation in the magnetic circuit was ob tained (where the areawas l5 mm?) when the airgap was 0.3 mm.

Preferably, those make contacts of the contact spring groups belongingto the relay, the closure of which is most delayed (close last) shouldbe operated when the airgap has that size.

During the continued movement of the armature towards the yoke (furtherdecreasing airgap) a very high saturation in the yoke and the armaturecan be allowed without any risk of interruption of the movement of thearmature.

What we claim is: I

1. An electromagnetic circuit adapted for use in a miniature relaycomprising: a yoke; a magnetizing coil; and a movable, elongate armaturedisposed inand through the longitudinal center channel in said coil;said yoke being of substantially flat shape with two spaced-apartparallel end portions and at least one side portion adjoining an end ofeach of said end portions to. provide said flat yoke shape with a spacebetween said end portions; said coil being placed in the yoke space sothat said coil channel and said armature, which is disposed through thecoil channel, are situated substantially adjacent one side of said flatyoke with one end of said armature placed and pivoted against one endportion of said yoke and the other end of said armature projecting fromsaid coil to a position adjacent said other end portion of said yoke toprovide a working airgap between the other end of said armature and theother end of said yoke situated outside of said coil.

2. An electromagnetic circuit according to claim 1, characterized by thefact, that the part of the armature (2) which is situated adjacent tothe airgap (7) is broaderthan the rest of the armature and that thedifference in width of said parts of the armature is so great, thatmagnetic saturation is obtained in the narrower part of the armature 2which is located inside the coil.

3. An electromagnetic circuit according to claim 2, and forming a partof an electromagnetic relay, characterized by the fact that a relativelyhigh magnetic saturation is obtained when the most delayed relaycontacts are operated by the movement of the armature, when the properpower for obtaining normal temperature rise (around 45 C.) is suppliedto the coil.

4. An electromagnetic circuit as defined in claim 1, wherein said coilincludes a bobbin with retention projections on each end; said yoke, inassembly on said bobbin engages said projections; a clip cooperates withthe end of said bobbin opposite the end where the working airgap islocated and with one end portion of said yoke to press said pivoted endof said armature against the said bobbin projection on the end of saidbobbin adjacent said clip.

5. An electromagnetic circuit according to claim 6, including a coilbobbin characterized by the fact, that the end of the I coil bobbinwhere the airgap 7 of the relay is located, is provided with aprojection 8 against which the outer end of the armature 2 falls whenthe relay is released, and that said projection 8 together with theinner bottom surface of the longitudinal opening through the coilbobbin, against which the other parts of the armature fall when therelay is released, has a damping effect on the movement of the armatureand prevent bouncing of the armature.

6. An electromagnetic circuit as defined in claim 1, wherein said yokehas only one elongate side portion and is shaped to provide a flatplanar U-shaped member with the coil nested in the space between the endportions and against the side portio 5 An electromagnetic circuit asdefined in claim 1, wherein said yoke has two parallel side portions andis shaped like a flat planar box frame which encompasses the said spacebetween the said yoke end portions.

1. An electromagnetic circuit adapted for use in a miniature relaycomprising: a yoke; a magnetizing coil; and a movable, elongate armaturedisposed in and through the longitudinal center channel in said coil;said yoke being of substantially flat shape with two spaced-apartparallel end portions and at least one side portion adjoining an end ofeach of said end portions to provide said flat yoke shape with a spacebetween said end portions; said coil being placed in the yoke space sothat said coil channel and said armature, which is disposed through thecoil channel, are situated substantially adjacent one side of said flatyoke with one end of said armature placed and pivoted against one endportion of said yoke and the other end of said armature projecting fromsaid coil to a position adjacent said other end portion of said yoke toprovide a working airgap between the other end of said armature and theother end of said yoke situated outside of said coil.
 2. Anelectromagnetic circuit according to claim 1, characterized by the fact,that the part of the armature (2) which is situated adjacent to theairgap (7) is broader than the rest of the armature and that thedifference in width of said parts of the armature is so great, thatmagnetic saturation is obtained in the narrower part of the armature 2which is located inside the coil.
 3. An electromagnetic circuitaccording to claim 2, and forming a part of an electromagnetic relay,characterized by the fact that a relatively high magnetic saturation isobtained when the most delayed relay contacts are operated by themovement of the armature, when the proper power for obtaining normaltempErature rise (around 45* C.) is supplied to the coil.
 4. Anelectromagnetic circuit as defined in claim 1, wherein said coilincludes a bobbin with retention projections on each end; said yoke, inassembly on said bobbin engages said projections; a clip cooperates withthe end of said bobbin opposite the end where the working airgap islocated and with one end portion of said yoke to press said pivoted endof said armature against the said bobbin projection on the end of saidbobbin adjacent said clip.
 5. An electromagnetic circuit according toclaim 6, including a coil bobbin characterized by the fact, that the endof the coil bobbin where the airgap 7 of the relay is located, isprovided with a projection 8 against which the outer end of the armature2 falls when the relay is released, and that said projection 8 togetherwith the inner bottom surface of the longitudinal opening through thecoil bobbin, against which the other parts of the armature fall when therelay is released, has a damping effect on the movement of the armatureand prevent bouncing of the armature.
 6. An electromagnetic circuit asdefined in claim 1, wherein said yoke has only one elongate side portionand is shaped to provide a flat planar U-shaped member with the coilnested in the space between the end portions and against the sideportion.
 7. An electromagnetic circuit as defined in claim 1, whereinsaid yoke has two parallel side portions and is shaped like a flatplanar box frame which encompasses the said space between the said yokeend portions.